The present invention relates to a modified polyolefin resin, and more particularly to a modified polyolefin resin which comprises a crystalline polyolefin, and a vinyl polymer prepared by a polymerization in the presence of the crystalline polyolefin specific in a manner so as to be dispersed in the fine particle form in the crystalline polyolefin as a matrix and to be at least partially grafted to the polyolefin, and which can improve the melting property of various other polyolefins, thus having an excellent effect of improving processability of other polyolefins. The present invention also relates to a polyolefin composition containing a polyolefin and the modified polyolefin resin, and more particularly to a polyolefin composition having excellent properties such as processability, impact resistance, rigidity and surface properties and being suitably applicable to the production of various molded articles.
Polyolefins have been widely utilized in various molded articles, since they are inexpensive and are superior in physical properties. However, they have problems.
For example, polypropylene has drawbacks that it is poor in processability such as thermoformability of the sheet (hereinafter referred to as "thermoformability"), calendering, blow moldability and expansion moldability since the melt viscosity and the melt tension are small, and that it is poor in rigidity as compared with polystyrene, polyvinyl chloride, ABS resin and the like, and that it is also poor low temperature impact resistance, surface properties such as gloss and hardness, and coatability.
In order to improve the processability of polypropylene, polyethylene has been generally incorporated into polypropylene by mechanical mixing. However, since the processability improving effect of polyethylene is insufficient, a large amount of polyethylene is required for this purpose, thus resulting in lowering of rigidity.
It is attempted to raise the melt viscosity and melt tension of polyolefins by increasing the molecular weight. However, use of polyolefins having a high molecular weight encounters a serious problem that they are difficult to be processed by extrusion which is one of important processing methods therefor.
It is proposed in U.S. Pat. No. 4,156,703 to improve the processability of polyethylene by adding a non-crosslinked acrylic polymer thereto. However, since compatibility between them is not sufficient and since the acrylic polymer added is non-crosslinked, the acrylic polymer separates from polyethylene when processed by calendering or extrusion, and it adheres to the surface of a calender roll or the surface of an extrusion die (this phenomenon being hereinafter referred to as "plate out"). Thus, the processability rather lowers.
For the purpose of improving the processability such as thermoformability of polypropylene, it is proposed in Japanese Patent Publication Kokai No, 2-22316 to add to polypropylene a mixture of a polyolefin, a methacrylate polymer and a polyolefin-methacrylate graft copolymer, which is obtained by polymerizing a methacrylic acid ester monomer in the presence of the polyolefin in a hydrocarbon solvent. However, this proposal has drawbacks that a large amount of the mixture is required for sufficiently exhibiting the effect of improving the processability, problems in preparation cost and safety arise since a solution polymerization at high temperatures is adopted, and the workability and safety are inferior since the solvent must be removed from the polymerization reaction mixture before adding to polypropylene.
Improvement processability such as thermoformability of polypropylene is also proposed in Japanese Patent No. 1,241,800 wherein polymer particles, as disclosed in Japanese Patent No. 1,219,793, prepared by polymerizing a vinyl monomer in the presence of polypropylene particles in an aqueous suspension at a temperature at which the polypropylene is not substantially molten, are added to a polypropylene in order to improve its processability. The polymer particles proposed as a modifier are characterized in that when they are blended with a polypropylene to be improved, fine dispersed units of the produced vinyl polymer in the modifier are uniformly dispersed in the resulting blend without agglomeration. However, the compatibility of the proposed modifier with polypropylene is insufficient, and the processability of polypropylene is not sufficiently improved by mere uniform dispersion of fine vinyl polymer units into the polypropylene.
Further, in order to improve impact resistance of polyolefins, a rubber component such as ethylene-propylene rubber has been generally introduced by mechanical mixing or block copolymerization. However, this method has the drawbacks that since it is difficult to control the size of particles to be dispersed in the polyolefins, the efficiency in use of the rubber component is low, thus the effect on improvement of impact resistance is not sufficiently exhibited, and that for such a reason, a large amount of the rubber component is required, so the rigidity of the obtained mixture is decreased. Also, the particle size of the dispersed rubber component is large, so the surface gloss of molded articles is lowered.
Core-shell modifiers which have been widely used as impact modifiers for vinyl chloride resins and the like, can cause to efficiently disperse a rubber component (core phase) having a predetermined particle size into matrix polymers, thus the impact resistance of the matrix polymers can be improved with preventing the rigidity from lowering. However, these core-shell modifiers have the problem that they are poor in compatibility with polyolefins which are non-polar, and they are hardly applicable to polyolefins.
Accordingly, it has been proposed to apply the core-shell modifiers to polyolefins in the presence of specific compatibilizers, as disclosed in Japanese Patent Publication Kokai No. 3-185037 and U.S. Pat. No. 4,997,884. However, the process steps for preparing these compatibilizers are complicated, so the use of compatibilizers increases the cost and also makes the system complicated.
There has not yet been proposed a polyolefin or a polyolefin composition which satisfies all of properties such as processability, impact resistance, rigidity and surface properties.
Accordingly, it is an object of the present invention to provide a polyolefin or a polyolefin composition which can satisfy all of the above-mentioned properties.
A further object of the present invention is to provide a modified polyolefin which can improve the melting property of polyolefin resins without substantially impairing other properties thereof and accordingly is useful as a modifier for improving the processability of polyolefin resins.
Another object of the present invention is to provide a polyolefin composition containing the modified polyolefin, which has an excellent processability and provides polyolefin molded articles having excellent physical properties such as impact resistance, rigidity and surface properties.
These and other objects of the present invention will become apparent from the description hereinafter.